This invention relates generally to microencapsulation and, more particularly, to microencapsulation of solids and liquids in a water-insoluble protein coating.
Microencapsulation is the an of encapsulating or enclosing a core comprising a solid or liquid in a miniature package called a microcapsule. The encapsulating material or coating of the microcapsule may be of various thicknesses and may be more than one layer thick.
Microcapsules may range from sub-micron in size to several millimeters in size. Although they are often thought of as being smooth and spherical, their shape and surface texture may be quite irregular as determined by both the encapsulating process and the shape and nature of the core material.
In the food industry, for example, microencapsulation is used to stabilize the core material, to control the timing and rate of the release of the core material and to separate reactive or incompatible components of a multicomponent formulation. Thus, microencapsulation makes it possible to protect sensitive food components, to ensure against nutritional loss and to mask or preserve flavors and aromas. Encapsulation also increases stability of vitamin supplements, for example, which are normally sensitive to UV radiation, light, oxygen, metals, humidity and temperature. Microencapsulation is also utilized in the pharmaceutical industry to protect the lining of the mouth and esophagus from harsh, orally administered drugs which are released in the stomach by the action of stomach acids on the microcapsule coating.
Spray drying is one of the most widely used methods of microencapsulation. This process, which involves dispersion and atomization, has a number of drawbacks. One disadvantage of the spray drying microencapsulation technique is that when heat is used for drying, low-boiling point aromatics are lost during the drying process. Another disadvantage is that the core may adhere to the surface of the capsule, presenting a potential for increased oxidation and changes in the flavor balance of the finished food product. Yet another drawback is that the coatings produced ace often water-soluble and temperature sensitive.
Extrusion is an encapsulation method in which a core material is dispersed in an amorphous mass of coating material and ultimately formed into microcapsule. One such method, described in U.S. Pat. No. 4,230,687 which is assigned to the assignee of the present invention, involves a microencapsulation technique in which the core material is mixed with the coating material under conditions of rigorous and intimate mechanical working in the presence of a limited quantity of water and sufficient heat to ensure the formation of a viscous semi-solid homogeneous paste constituting a plastic melt. The melt, which is a homogeneous matrix of the encased core material is formed into a desired shape and dried. The coating agent is a water-soluble or water-dispensable material such as a carbohydrate like dextrin, gum acadia and gum karaya, or a protein like gelatin (water soluble at about 160.degree. F.) or sodium caseinate.